Bcl-xL is a 29 kDa member of the Bcl-2 family of proteins involved in regulation of programmed cell death, or apoptosis. It is found in both soluble and membrane fractions of cellular lysates. Like Bcl-2, Bcl-xL has been demonstrated to block apoptosis which is induced by a variety of stimuli and, under certain conditions, offers greater protection against apoptosis than Bcl-2. While formation of heterodimers with the apoptosis-enhancing protein, Bax does not block the apoptosis-suppressing property of Bcl-xL, heterodimerization with Bad effectively inhibits the protective function of Bcl-xL.